Electron focusing systems and techniques integrated with a scintillation detector covered with a reflective coating

ABSTRACT

The present disclosure provides systems and methods where an electron focusing device can be combined with a scintillation detector to better focus the electrons generated by a light sensing device. The scintillation detector can include a scintillation crystal that is covered by an inner light-reflecting coating layer where the scintillation crystal may emit photons due to measurement radiation(s). The light sensing device can include a photomultiplier that may receive the photons emitted by the scintillation crystal and convert them into the electrons generated. The electron focusing device can include a metal ring magnet or one or more conducting coils encircling the scintillation crystal that may create a magnetic field so as to focus the electrons generated by the light sensing device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/243,575.

FIELD

This disclosure relates generally to electron focusing systemsintegrated with scintillation detectors and methods for performingradiation-based measurements using the systems and methods ofmanufacturing the system particular the scintillation detectors. Thesystems and techniques described herein are particularly useful forborehole logging applications.

BACKGROUND

Scintillation detectors have been employed in the oil and gas industryfor well logging. These detectors have used thallium activated sodiumiodide crystals that are effective in detecting gamma ray radiations.The crystals are enclosed in tubes or casings to form a crystal package.The crystal package has an optical window at one end of the casing,which permits scintillation light induced by radiation to pass out ofthe crystal package for measurement by a light sensing device such as aphotomultiplier tube coupled to the crystal package. The photomultipliertube converts the light photons emitted from the crystal into electricalpulses that are shaped and digitized by associated electronics.Therefore, the fraction of the induced scintillation light collected bythe photomultiplier should be as large as possible. One reason, whichleads to reduce this fraction of light, is the losses at the crystalsurface. The uniformity of light collection depends primarily on theconditions, which exist at the interface between the crystal and theenclosing tube. In order to recapture the light that escapes from thesurface, the crystal is normally surrounded by a reflector at allsurfaces except that at which the photomultiplier tube is mounted. Twotypes of reflector can be used: a polished metallic surface acting as aspecular reflector or a dry powder packed around surfaces of the crystalacting as a diffuse reflector.

The ability to detect gamma rays makes it possible to analyze rockstrata surrounding the borehole, as by measuring the gamma rays comingfrom naturally occurring radioisotopes in downhole shales which boundhydrocarbon reservoirs. A common practice is to make those measurementswhile drilling (MWD); and for this type of application, the detectormust be capable of withstanding high temperatures and also must havehigh shock resistance. At the same time, there is a need to maintainperformance specifications.

A problem associated with MWD applications is that the reflector used inthe detector, specular or diffuse, will suffer from those hightemperatures and high shocks. When a diffuse reflector as a dry aluminumpowder is used, after some shocks it will clog at one end of the crystalpackage and fail to reflect light at all surfaces. And when a specularreflector as polytetrafluoroethene (PTFE) tape, or any type of foil isused, the inhomogeneities of the crystal edge do not ensure a perfectcontact between the crystal and the foil. Air and gas are irremediablytrapped in the crystal/foil interface and it does not permit to the foilto act as a perfect specular reflector, reducing a large fraction oflight induced by the crystal.

Another problem associated with MWD applications, is that detectorsreport a higher than an actual count rate if the scintillation crystalpackage produces vibration induced light pulses. The harsh shock andvibration conditions the detectors encounter during drilling can cause acrystal package to emit spurious light pulses in addition to gamma rayinduced light pulses. That is, the detector output will be composed ofradiation induced counts and vibration induced counts. Heretofore, thedetector electronics could not distinguish the vibration induced countsfrom the genuine gamma counts, whereby the detector reports a higherthan actual count rate. Some prior art solutions use electronic devicesto filter out vibration induced counts by discriminating on the basis ofthe pulse shape and/or the signal decay time. Other solutions, directlyapplied to the package of the crystal, described in U.S. Pat. No.5,869,836, use an elastomeric material which absorbs shocks andvibration. Commonly, this elastomeric material is associated with a PTFEtape to act as a reflector. This shock absorbing member solves theproblem related to high temperatures and high shock resistance, but notto the problem of specular reflector. The present disclosure provides asolution to the aforesaid problem of reflector in the crystal package.

SUMMARY

The present disclosure provides systems and methods where an electronfocusing device can be combined with a scintillation detector to betterfocus the electrons generated by a light sensing device. Thescintillation detector can include a scintillation crystal that iscovered by an inner light-reflecting coating layer via a chemical and/orphysical binding where the scintillation crystal may emit photons due tomeasurement radiation(s). The light sensing device can include aphotomultiplier that may receive the photons emitted by thescintillation crystal and convert them into the electrons generated. Theelectron focusing device can include a metal ring magnet or one or moreconducting coils encircling the scintillation crystal that may create amagnetic field so as to focus the electrons generated by the lightsensing device.

In a preferred embodiment, the chemical binding is realized by achemical vapor deposition process, called CVD. The CVD ensure anexcellent adhesion to the crystal and a uniform thickness, even in deepholes and recesses.

In another preferred embodiment, the physical binding is realized by aphysical vapor deposition process, called PVD. The PVD does not affectthe dimensions and geometry of the crystal while ensuring a goodadhesion to the crystal and, a uniform and homogenous layer. Theuniformity, the composition and the structure of the coating layer canbe optimized and parameterized separately. Preferably, the PVD will bedone by sputtering.

Preferably, the inner coating is thermally conductive. The thermalconductivity ensures a good heat transfer inside the crystal, so thatthe temperature on the coating layer and crystal interface ishomogenous, and also inside the crystal.

Preferably, the inner coating is electrically conductive. The electricalconductivity of the coating layer avoids the triboelectric effect.

In a preferred embodiment, the crystal is a sodium iodide crystalactivated with thallium NaI(Tl) and the inner coating is done with ametal such as aluminum.

The emission spectrum of NaI(Tl) presents a peak at 410 nm and aluminumpresents perfectly good reflection properties in this UV region of thelight spectrum.

In a preferred embodiment, the scintillation detector further comprisesan outer coating layer, this outer coating layer being stuck directly tothe inner coating layer by a chemical and/or a physical binding. Theouter coating layer can cover all the surface of the inner coating layeror a partial one's. The process used to create the physical and/orchemical binding is the same as for the inner coating layer. In apreferred embodiment the outer coating is done with a metal such asplatinum or gold. The second coating layer will enhance the reflectionproperties of the first coating layer.

In a preferred embodiment, the scintillation detector further comprisesa shock absorbing member covering the inner coating layer or the outercoating layer if present. The shock absorbing member is made of anelastomeric material which protects scintillation crystal against shockand vibrations.

According to a further aspect, the disclosure provides a method ofmeasuring radiation from an environment including the steps of:

-   -   positioning in the environment the system described above,    -   receiving emitted photons from the scintillation crystal with        the light sensing device,    -   converting the emitted photons into electrical signals        comprising a plurality of electrons, wherein the electrical        signals substantially represent the radiation being measured,        and    -   generating a magnetic field using the electron focusing device        so as to focus the plurality of electrons.

In a preferred embodiment, the light sensing device is aphotomultiplier.

According to a still further aspect, the disclosure a method ofmanufacturing the system described above, wherein the scintillationdetector is made by a method comprising the steps of:

-   -   defining two surface parts in the scintillation crystal: first        and second parts,    -   covering said first part of said scintillation crystal with the        inner coating layer, where said inner coating layer is        reflective to light spectrum and said inner coating layer is        deposited onto said crystal by a chemical and/or a physical        binding, leaving said second part without coating,    -   positioning said scintillation crystal and said inner coating        layer in a shock absorbing member,    -   positioning said second part in front of an optical window        transmissive to scintillation light given by said scintillation        crystal,    -   positioning said shock absorbing member and said optical window        in a protective housing.

Preferably, the method of manufacturing the system, further comprisesthe step of covering said inner coating layer with an outer coatinglayer, wherein said outer coating layer is deposited onto said innercoating layer by a chemical and/or a physical binding.

In a preferred embodiment, the chemical binding is realized by CVDand/or the physical binding is realized by PVD.

Preferably, the inner and/or outer coating layer is thermally conductiveand/or is electrically conductive.

Preferably, the inner and/or outer coating layer is made of metal. Whena sodium iodide crystal activated with thallium is used as scintillationcrystal: the inner metal layer is aluminum and the outer metal layer isplatinum or gold.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of a scintillation crystal package in accordance withthe present disclosure.

FIG. 2 is a cross-sectional view of the scintillation crystal packagetaken along the line 2-2 of FIG. 1.

FIG. 3 is an example where an electron focusing device is combined witha scintillation detector.

FIG. 4( a)&4(b) illustrate two examples where magnetic fields can begenerated using electron focusing devices.

FIG. 5 shows the effects of PMT, scintillation crystal and magneticfield on “edge electrons.”

DETAILED DESCRIPTION

Referring now in detail to the drawings, FIGS. 1 and 2 illustrate anexemplary and preferred scintillation crystal package 10 according tothe present disclosure. Package 10 comprises of a scintillation crystal12, which is covered with an inner primary coating layer 14, thisprimary coating layer 14 covering all the surface of the crystal exceptthe front-end face 11 of the crystal. In the illustrated preferredembodiment, the scintillation crystal 12 has the shape of a rightcylinder. It is contemplated that this disclosure may have applicationto crystals of other shapes and the layers may be applied to a crystalsurface other than a cylindrical surface. Scintillation crystal 12 is asodium iodide crystal activated with thallium NaI(Tl). NaI(Tl) is anexcellent light yield to primary or secondary electrons; because itsresponse to electrons and gamma rays is close to linear over most of thesignificant energy range. The primary coating layer 14 is made ofaluminum; because the emission spectrum of NaI(Tl) presents a peak at410 nm and aluminum presents perfectly good reflection properties inthis UV region of the light spectrum. The thickness of the coating layer14 is of some microns, preferably 1 to 4 microns.

The primary coating layer 14 has also a good thermal conductivity. Thethermal conductivity ensures a good heat transfer inside the crystal, sothat the temperature on the coating layer and crystal interface ishomogenous, and also inside the crystal. This good thermal conductivityavoids transient temperature distribution, which brings about transientdecay time in induced crystal's fluorescence. To ensure a good timeresolution of the scintillation detector, this decay time must be kepthomogenous inside the crystal. For NaI(Tl) dominant decay time of thescintillation pulse is 230 ns at 20° C. When temperature is higher, thedecay time decreases.

The primary coating layer 14 has also a good electrical conductivity.The electrical conductivity of the coating layer avoids thetriboelectric effect. Effectively, when a specular reflector aspolytetrafluoroethene directly circumscribes the crystal, shocks andtemperature variations generate friction at the interfacepolytetrafluoroethene/crystal, which leads to electrically charging thepolytetrafluoroethene and the crystal. When discharging, inducedscintillation light will be created inside the crystal. That is, thedetector output will be composed of the triboelectric induced counts.And heretofore, the detector electronics could not distinguish thetriboelectric induced counts from the genuine gamma counts, whereby thedetector reports a higher than actual count rate. When a conductivecoating layer is used no triboelectricity can be generated.

In the illustrated preferred embodiment, the primary coating layer 14 iscovered by an outer second coating layer 16. In the preferredembodiment, this second coating layer 16 covers all the surface of theprimary coating layer 14. The second coating layer 16 is made ofplatinum, because of its good reflective properties and non-corrosiveproperties versus aluminum. The thickness of the second coating layer 16is of some microns, preferably 1 to 3 microns. The second coating layerwill enhance the reflection properties of the first coating layer. Someof the induced scintillation light in the crystal may be attenuated andwill have undergone multiple reflections, losing each time a fraction ofthe output light. The second coating layer will reflect photons thatwere lost after the first coating layer. In the preferred embodiment,the second coating layer 16 is made of a material further having goodthermal conductivity and good electrical conductivity to maintainadvantages already explained for primary coating layer.

In the preferred embodiment represented in FIGS. 1 and 2, the crystal 12and the two coating layers (14, 16) are surrounded by a shock absorbingboot 18, which in turn is surrounded by a casing 20. The shock absorbingboot 18 is made so that the crystal 12 is loaded within a housing, whichprovides sufficient stiffness such that the operational dynamicbandwidth of the detector application falls below the resonant frequencyof vibration induced counts. Therefore, within that environment,vibration induced counts will either not occur or will have a magnitudethat falls below an amplitude threshold and will be ignored. The shockabsorbing boot 18 is finally and preferably constrained in the casing 20to ensure hermetic contact from environment. Because, NaI(Tl) ishygroscopic and will deteriorate due to water absorption when exposed tothe atmosphere, the crystal 12 must therefore be constrained in anair-tight container from exposure to the surrounding environment. Thecasing 20 is closed at its rear end by a back cap 22 and at its frontend by an optical window 24. The optical window 24 should be made of amaterial transmissive to scintillation light given off by thescintillation crystal 12, as for example crown glass. The casing 20 andback cap 22 are made preferably of stainless steel or aluminium, as isconventional. The back cap 22 and optical window 24 have sandwichedtherebetween, going from left to right in FIG. 1, a spring 26, a packingplate 28, the boot 18, the crystal 12 and the two coating layers (14,16) and an interface pad 30. The spring 26, or other suitable resilientbiasing means, functions to axially load the crystal and press ittowards the optical window 24. The spring 26 is a stack of wave springsdisposed crest-to-crest. The spring 26 resiliently pushes the crystal 12towards the optical window 24 to maintain an optical coupling betweenthe front-end face 11 of the crystal 12 and the interface of the opticalwindow 24, thanks to the interface pad 30. The interface pad 30 is madeof a suitable optical coupling material such as a transparent siliconeelastomer pad sandwiched between the crystal 12 and the optical window24. As shown, the boot 18 occupies the space between the packing plate28, the casing 20, the interface pad 30 and the crystal 12 and the twocoating layers (14, 16). The boot 18 is preferably cylindrical andconcentric with the crystal 12 and the casing 20. The boot 18 is made ofresiliently compressible material and preferably is a silicone rubber,elastomer, or silicone elastomer. The silicone elastomer does notinclude preferably any fillers such as reflecting material powder thatmay degrade performance.

In another embodiment of this disclosure not shown on the Figures, theinner or outer coating layer can further comprise miniaturized andlow-power electronics such as:

-   -   a temperature sensor to measure the temperature in the inner or        outer coating layer and therefore in the crystal,    -   a heating or a cooling device to control the temperature of the        crystal,    -   a diode or a piezoelectric generator to emit quantities of light        at regular period; quantities of light that can be analyzed        after the photomultiplier by further electronics to calibrate        the scintillation crystal (time decay for example).

In some embodiments, an electron focusing system can be used with thecoated crystal described herein where a magnetic field may be generatedto re-focus the electrons leaving the photocathode, due to theillumination through the photons that are yielded from the gamma rayinteractions within the crystal. In some cases, the electron focusingsystem can include an electrical circuitry or conductive strip that isplaced close to the end of the crystal in contact with thephotomultiplier tube (PMT). When passing a current through thisconductive path, a magnetic field can be created, which in turn wouldfocus the “slower” electrons from the borders of the photocathode to thecenter and avoid “spurious” or thermally induced noise. In some cases,the electron focusing system can include a “permanent” axial magnet toreduce slightly the apparent surface of the photocathode (mostly on theborders, where it may greatly reduce thermally induced noise).Preferably, the electron focusing system is fitted onto the crystal,instead onto the PMT, as shown in FIG. 3.

In some embodiments, a static focusing magnetic field may be generatedby a metallic ring magnet located near the front window of the crystal,as shown in FIG. 4 a. A width of the metallic ring, R, that issubstantially equal to a radius of the crystal, φ/2, should be used tooptimize magnetic shielding or focusing.

In some embodiments, an adjustable focusing magnetic field may begenerated by a conducting coil wound around the crystal, possibly closeto the front window, as shown in FIG. 4 b. A current, I, passing throughthe coil can generate a focusing magnetic field, B, proportional to thecurrent, I. The magnetic field, B, generated on the inner surface of thecoil can be approximated by: B=μ₀NI, where B is the magnetic fieldgenerated (Tesla); N is the number of turns of the coil; I is thecurrent flowing through the coil (Ampere); and μ₀ is the permeabilityconstant (4π*10⁻⁷). The magnetic field, B, may alter the electroncollection between the photocathode and the first dynode, when the fieldstrength is typically greater than about a few Tesla/100 (e.g., 10 to 50milli-Telsa).

In some embodiments, the electron focusing system can be directlyintegrated onto the outer reflective coating of the crystal bysputtering a magnetic material thereon, with a relatively high magneticpermeability.

The axial magnetic field generated can “defocus” the electrons createdat the outskirts of the photocathode, which usually are not veryhomogenous in response to photons, thereby focusing the “slower”electrons from the borders of the photocathode to the center and avoid“spurious” or thermally induced noise. Following Laplace's law, theelectrons leaving the photocathode perpendicularly, in the direction ofthe magnetic field would not be affected. The electrons at the centerare primarily accelerated by the electric field generated between thephotocathode and the first dynode, via about 200 V/cm. Since q*v=I*dl,the force, F, exerted on a charge particle like an electron is given by:

${{F=={q*v*\Lambda \; B}} = {{\frac{d}{st}\left( {m*v} \right)} = {m*\gamma}}},$

where v is particle velocity vector; γ is particle acceleration vector;B is magnetic field vector; and q is charge of particle. When thecharged particles, e.g., the electrons generated and leaving thephotocathode, with a velocity parallel to the B field, the electronsshould not be deviated and should be slightly accelerated in the samedirection. For the spurious electrons, leaving the photocathode, usuallyat a lower speed at the outskirts of the photocathode, the magneticfield, B, can deviate the electrons to the sides so that they won'treach the first dynode.

Typical photocathodes are not homogenous on their circumferential edges;the closer to the center of the photocathode, the better is thehomogeneity of electron emission. The electrons generated by the edgesof the photocathodes are usually the major source of “dark current” whentemperature increases; some electrons may also be generated“spontaneously”, i.e., those electrons may not be due to the photonimpingement, but through the electron emission. The electrons generatedat the edges of the photocathodes typically are not all exactly directedperpendicularly to the photocathodes, and many thermally inducedelectrons may have an initial velocity with an angle θ with the magneticfield B. Such electrons can thus be deviated towards the walls, awayfrom the center of the first dynode, thereby causing lesser thermallyinduced noise before multiplication as seen in FIG. 5 where the initialdirection of the electrons in the center of the photocathode is andremains perpendicular to the surface, while on the edges the electronsgenerated may be deviated.

The systems and techniques described herein where an electron focusingsystem is combined a coated crystal provide several advantages,particularly at high temperatures. For a circular shaped photocathode,the center is quite homogenous and the electrons are more easilyattracted and focused by the electrical field generated by thedifference in voltage between the first dynode and the photocathode. Theedges of the circular shaped photocathode is not evenly sputtered (e.g.,several layers and adjustments may be used and the sputtering is usuallydone from a beat introduced on one side near the front end of the PMT(Photocathode). The electrons generated thereof can of two kinds: (1)The elelctrons generated by the photon impingement onto thephotocathode; and (2 the thermally induced electrons (also calledthermoionic noise), with relative lower kinetic energy (spontaneousemission), which are usually saturating the PMT and the counting withcounts increasing exponentially with temperature. For semiconductors,like the photocathode material, the lower potential barrier generatingthermal emissions can be of the order of 10⁶ to 10⁸ electrons/m²/second.As such, for PMT's having an extremely high gain, e.g., of the order of10¹⁰ to 10¹¹, electron multiplication may rapidly saturate theacquisition electronics with unwanted, superfluous, thermoionic noise.

In accordance with another aspect of this disclosure, a method isdescribed to measure radiation in a borehole environment using theaforementioned scintillation detector 10. A well logging tool, includinga downhole sonde is suspended in a borehole by a cable. The cableconnects the downhole sonde to surface equipment, including powersupply, surface electronics and post processing associated peripherals.The downhole sonde is positioned close to the environment to bemeasured. The scintillation detector 10 receives the natural gammaradiation or scattered gamma rays and induces scintillation photons. Alight sensing device, such as a photomultiplier, receives emittedphotons and converts the emitted photons into electrical signals. Theelectrical signals, after being processed, substantially represent theradiation being measured.

In accordance still with another aspect of this disclosure, a method isdescribed to manufacture the aforementioned scintillation detector 10. Acoating is performed onto a part of the surface of the NaI(Tl) crystal;and two types of process can be used: one by chemical vapor deposition(CVD) and second by physical vapor deposition (PVD).

When the CVD process is used a chemical binding is realized between thecrystal and the coating. The chemical vapor deposition is a successivechain of chemical reactions, which transform gaseous molecules, calledprecursor, into a solid material, in the form of thin film or powder, onthe surface of the crystal. During deposition, a thin film growths onthe surface of NaI(Tl) crystal. The CVD ensures an excellent adhesion tothe crystal and a uniform thickness, even in deep holes and recesses.The front-end face 11 of the crystal, which will be not coated, ismasked during the deposition with a resin or a mask holder.

When the PVD process is used a physical binding occurs between thecrystal and the coating. The physical vapor deposition consists invaporizing a solid material within a vacuum chamber and to migrate thesevaporized particles onto the crystal to form a thin film. Differenttypes of PVD are known depending on the driving force, which migrates tothe vaporized particles. In a preferred embodiment, the PVD will be doneby sputtering. The solid material is vaporized from an anode and willmigrate to a cathode thanks to an electric beam. The crystal will bepositioned between anode and cathode and a thin layer will be formedwhen vaporized particles will impact on the crystal. The PVD, becausethe temperature of the process is much lower compared to CVD (500° C.compared to 1000° C.), does not affect the dimensions and geometry ofthe crystal while ensuring a good adhesion to the crystal and a uniformand homogenous layer. For the preferred embodiment represented on FIGS.1 and 2, an aluminum thin film of 3 μm will growth on the surface ofNaI(Tl) crystal at a speed of approximately 1 μm per hour. The front-endface 11 of the crystal, which will not be coated, is masked during thePVD with a resin or a mask holder. The operation is repeated afterprimary coating with another coated material: a platinum thin film of 3μm is coated on the surface of the primary coating layer. The front-endface 11 of the crystal, which is still not coated, is masked with aresin or a mask holder. With the PVD process, the uniformity, thecomposition and the structure of the coating layer can be optimized andparameterized separately.

For the preferred embodiment represented on FIGS. 1 and 2, the coatedcrystal is positioned in the shock absorbing boot 18 and the boot isfinally compressed in a protective casing 20. The casing 20 provides awindow 24 and an optical coupling 30 between the scintillation crystaland the up coming photomultiplier tube.

In accordance with another aspect of this disclosure, other types ofgeometric layer can be performed when the PVD is done by sputtering. Asfor semiconductor engraving, it is possible thanks to predefined masksto coat all types of shape in two dimensions: a mask will define thepart that will be not coated. To perform shape in three dimensions, twodimensions shapes are build level per level with different masks tofinally perform a three dimensional model.

In a preferred embodiment, the outer coating layer has the shape of acoil and is electrically conductive, creating a solenoid directly stuckto the crystal surface. This coil will be engraved near the frontoptical window and can create a magnetic field when a current circulatesin the coil. This magnetic field ensures continuity with the magneticfield created by the photomultiplier tube, so that at the entrance ofthe photomultiplier tube, the total magnetic field induced is maximum.

1. A system, comprising: a scintillation detector comprising ascintillation crystal covered by an inner coating layer, said innercoating layer being reflective to light spectrum; a light sensing devicecapable of converting photons emitted by said scintillation crystal intoelectrical signals comprising a plurality of electrons; and an electronfocusing device comprising at least one conductive unit capable ofgenerating a magnetic field so as to focus at least a portion of saidplurality of electrons toward a central axis of the system.
 2. Thesystem of claim 1, wherein the at least one conductive unit comprises ametallic ring magnet encircling said scintillation crystal and having awidth substantially equal to a radius of said scintillation crystal. 3.The system of claim 1, wherein the at least one conductive unitcomprises one or more conducting coils winding around said scintillationcrystal.
 4. The system of claim 1, wherein the light sensing devicecomprises a photomultiplier.
 5. The system of claim 1, wherein saidscintillation crystal further comprising an outer coating layer; whereinsaid outer coating layer is deposited onto the inner coating layer by achemical and/or physical vapor deposition process.
 6. The system ofclaim 5, wherein at least one of the inner and outer coating layers isthermally conductive.
 7. The system of claim 5, wherein at least one ofthe inner and outer coating layers is electrically conductive.
 8. Thesystem of claim 7, wherein the inner coating layer is electricallyconductive; said system further comprising a shock absorbing memberhaving an elastomeric material and covering said inner and outer coatinglayers.
 9. The system of claim 5, wherein said scintillation crystal isa sodium iodide crystal activated with thallium; wherein said innercoating layer comprises aluminum and said outer coating layer comprisesplatinum or gold.
 10. The system of claim 1 further comprising a sensorto measure a temperature inside said scintillation crystal.
 11. Thesystem of claim 1 further comprising a device to control a temperatureinside the crystal.
 12. The system of claim 1 further comprising a lightemitter capable of emitting quantities of light at regular periods;wherein said quantities of light are analyzed to calibrate saidscintillation crystal.
 13. A method of measuring radiation from anenvironment, including the steps of: positioning in said environment, asystem as claimed in claim 1; receiving the emitted photons from thescintillation detector with the light sensing device; converting thephotons received into the electrical signals, wherein the electricalsignals substantially represent the radiation being measured; andgenerating a magnetic field with the electron focusing device to focusat least a portion of said plurality of electrons toward a central axisof the system.
 14. A method of manufacturing a system as claimed inclaim 1, wherein the scintillation detector is made by a methodincluding the steps of: defining two surface parts in the scintillationcrystal: a first part and a second part, wherein the scintillationcrystal comprises a sodium iodide crystal activated with thallium;covering said first part of said scintillation crystal with the innercoating layer that is electrically conductive, leaving said second partwithout coating; covering said inner coating layer with an outer coatinglayer comprising platinum or gold, wherein said outer coating layer isdeposited onto said inner coating layer by a chemical and/or a physicalvapor deposition process; positioning said scintillation crystal andsaid electrically conductive inner coating layer in a shock absorbingmember comprising an elastomeric material; positioning said second partin front of an optical window transmissive to scintillation light givenby said scintillation crystal; and positioning said shock absorbingmember and said optical window in a protective housing.